I can't imagine that anything will penetrate down far enough to help if the post is seized. Whack the post with a hammer, ie further into the seat-tube. That might free it up.
Or, heat the seat tube up as much as you can. It should expand slightly and loosen the grip. Problem there is applying enough heat without knackering the paint. Alu shouldn't need too much heating though. It may be that an electric fan heater blasting it for a while may be enough to give you that extra movement, or at least create more of a gap to allow a lubricant to capilliary-action it's way down the tube.
On the lube front. I was told to remove the seat post monthly to prevent seizing. That's why my post came with one of those little plastic clamp gizmos that marks your seat height, allowing for easy removal and re-setting.